The invention relates to a coaxial valve for regulating and shutting off the flow of a fluid or gaseous flow medium.
There are particularly stringent requirements for valves which are used for regulating and shutting off liquid or gaseous flow media under extreme conditions such as chemical aggressiveness, very high or very low temperatures or very high pressures. Propulsion in aircraft and spacecraft is one field of application of valves used for shutting off a liquid or gaseous medium under extreme conditions. In such applications, the valves are subjected not only to extreme high and low temperatures but also to extreme temperature changes. In the case of valves for liquid and gaseous rocket fuels, there are further parameters such as high mass flow rates, high pressures and short switching times (opening, closing, positioning).
For use in particular in aerospace applications, a coaxial valve is used for shutting off a liquid or gaseous flow medium, comprising a valve housing, a valve sleeve, and a closing body. The valve housing has an inlet and an outlet for the medium to be shut off. The valve sleeve is arranged in the valve housing in an axial direction between an open position and a closed position, whereby the valve sleeve is slidable in a longitudinal direction of the valve housing between the open and closed positions for the purpose of opening or shutting off the flow of the medium. The medium to be shut off flows in the longitudinal direction through the valve sleeve when the valve is open. The closing body is arranged at one end of the valve sleeve coaxially thereto. The valve sleeve rests against the closing body in the closed position so as to provide a seal, and on the other hand, with the valve sleeve in the open position, the valve sleeve is spaced at a distance from the closing body for freeing a valve opening cross section therebetween. Such a coaxial valve further comprises an actuating drive for opening and closing the valve.
Up to now, valves of the above described type comprised a pneumatically operated actuating drive. A pneumatic system such as the actuating drive of a valve has the disadvantage in that it is very complex, is associated with the danger of leakage, and in particular in aerospace applications is problematic in view of the high reliability which is required. Possible leakage is conducted away separately in a connecting line.
Helium is used as a pressure means (control fluid) which is used primarily as a seal gas between the hot and the cold flow (turbine propellant gas/fuel) in the turbopumps and during such use is consumed due to leakage losses. It can thus happen that toward the end of a mission there is no longer any helium left for operating the valves. A further disadvantage is the expenditure in design, weight and cost, required for the helium pipe system and regulating system to which each fuel valve has to be connected. Such systems also pose problems concerning their reliability. Since a compressible gas is used as a pressure medium, the actuation movement of a valve can only be very coarsely influenced from a time-related and kinematic point of view. Only an open position and a closed position are possible, both against an end stop. Defined intermediate positions and precise control movements are practically impossible.
German Utility Model DE 297 06 688 U1 discloses a coaxial valve as mentioned above, further including a transmission part in the form of a lever or an articulated lever which is used as a connection between an actuator and a valve sleeve and which causes displacement of the valve sleeve in the coaxial valve. In this arrangement, the transmission part interacts on one side with the valve sleeve. With such an arrangement there is an inherent danger that due to the one-sided application of force, the valve sleeve may jam in the coaxial valve. This is particularly fatal for applications where maintenance of the coaxial valve is not possible or possible only at considerable expense, such as for example during the extreme conditions mentioned in the introduction.
European Patent Application Publication EP-OS 0 257 906 discloses various embodiments of seat valves in which the axially-movable seat body is driven by an electric motor via a spindle/nut arrangement. The emphasis has been placed on achieving as compact a design of the valve housing as possible. This has been achieved in that the rotor of the electric motor largely makes use of the cross section of the flow channel, with the rotor itself being located in the flow stream of the conveying medium. In this way, the external diameter of the valve housing corresponds approximately to the external diameter of the adjoining pipelines. Such an arrangement is however associated with considerable disadvantages. The units (bearing, rotor, gearing) which are incorporated directly in the flow channel, considerably impair the flow, so that considerable losses in pressure have to be anticipated. Depending on the physical characteristics of the flowing medium, large friction moments act on the rotating rotor, so that an unnecessarily increased amount of power is required to drive it. Aggressive flow media can chemically/physically attack bearings, rotor and gearing, and thus considerably shorten their useful life. Consequently, such a valve design is only suitable for non-aggressive media of low viscosity, where the throughput is relatively small.
It is an object of the present invention to provide a control valve, in particular for cryogenic and aggressive rocket fuels, which is particularly flow-enhancing, relatively simple and compact in design, and which has a drive that is not located in the conveyed flow medium. Furthermore, the drive should be arranged so as to be largely thermally decoupled, and it should consume as little power as possible. In addition, operation of the control valve is to be as troublefree as possible. The invention further aims to avoid the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a coaxial valve for regulating and shutting-off the flow of a liquid or gaseous flow medium. The valve comprises a valve housing with an inlet and an outlet connected by a flow passage for the liquid or gaseous medium, and a valve sleeve that is arranged in the housing (in the flow passage) axially between an open position and a closed position, so as to be slidable in a longitudinal direction between the open position for allowing the medium to flow in the longitudinal direction through the valve sleeve, and the closed position for shutting off the flow of the medium. The valve further comprises a closing body that cooperates with the valve sleeve to selectively achieve the closure seal or the open flow passage through the valve. Particularly, on the one hand the valve sleeve rests against the closing body in the closed position to provide a seal, and on the other hand, when the valve sleeve is in the open position, the sleeve is spaced at a distance away from the closing body so as to free a valve opening cross-section. The present valve further comprises an actuating drive for opening and closing the valve by sliding the valve sleeve selectively in the longitudinal direction between the open position and the closed position and/or to any desired intermediate partial-open position therebetween.
Particularly according to the invention, the actuating drive comprises a rotational electric servomotor including a linear actuator, and a transmission part or mechanism coupled between the linear actuator and the valve sleeve so as to transmit the linear movement of the linear actuator to the valve sleeve. The transmission part or mechanism comprises an adjusting lever embodied as a rocking lever that extends in a direction generally transverse relative to the longitudinal direction of motion of the valve sleeve. A first end of the rocking lever or adjusting lever is articulately connected by a drive bearing to the linear actuator of the servomotor, while the second end of the adjusting lever is articulately coupled by a locating bearing to the valve housing, and a middle section of the adjusting lever between the first and second ends is articulately connected by an actuator bearing to the valve sleeve. With such an arrangement, the adjusting lever transmits the linear motion of the linear actuator of the servomotor to a linear motion of the valve sleeve, while accurately transmitting the driving force along the linear path of the motion of the valve sleeve and avoiding alignment errors and the like between the valve axis and the drive axis. The two opposite ends of the adjusting lever are slidable and articulated respectively in the drive bearing and the locating bearing, while the middle section of the adjusting lever is articulated via the actuator bearing to the valve sleeve.
One advantage of the coaxial valve according to the invention is its high reliability even under extreme conditions. A further advantage consists of one valve sleeve being pressure-equalized, thus requiring only modest actuating power. Another advantage consists of its flow shape with the seal seat being easily adjustable and exchangeable.
A further advantage of the coaxial valve according to the invention consists of it being steplessly adjustable with high precision between the open position and the closed position. Yet another advantage consists of its actuating time between the open position and the closed position or from a defined position to another defined position being freely selectable. A still further advantage of the coaxial valve according to the invention consists of it being electrically controllable in a simple way. There is another advantage in that, in contrast to pneumatically controlled valves, no leakage problems can occur. Furthermore, it is a significant advantage of the coaxial valve according to the invention in that it can easily be electrically implemented in various environments. No screws can fall into the flow medium space, and the coaxial valve can easily be flushed out with gas. In this way, the danger of freezing during operation with cryogenic media can be avoided.
The special type of the adjusting lever in the form of a rocking lever and the way it is held and arranged, in particular via coupling with the valve sleeve in a middle region, reduces the danger of the valve sleeve jamming. This is because, in contrast to the prior art, impingement or coupling of force on the valve sleeve so as to move the valve sleeve is now not merely on one side, but instead the coupling of drive forces onto the valve sleeve from several sides is possible.
De-coupling of the electric drive from radial pressure and shrinking forces is ensured. Furthermore, constraining forces as a result of alignment errors between the valve axis and the drive axis are avoided.
A preferred embodiment of the invention provides for the actuator of the servomotor to be movable co-linear or parallel to the longitudinal direction of displacement of the valve sleeve.
Another preferred embodiment of the invention provides for the actuator bearing to comprise an actuator cog or journal pin provided on the exterior of the valve sleeve, and a bearing bore that is provided in or on the adjusting lever and that accommodates the actuator cog therein. In this arrangement, the force is introduced over a large area into the thin-walled sliding sleeve. Also, manufacturing expense is reduced due to a simple shape and a reduced number of parts.
An alternative embodiment provides for the actuator bearing to be formed by a ball surface provided on the exterior of the valve sleeve, and by a socket surface provided on the adjusting lever, whereby the socket surface accommodates the ball surface.
A preferred improvement of the invention provides for the adjusting lever in the region of the actuator bearing to be configured so as to surround the valve sleeve, e.g. with two portions of the lever extending respectively around opposite sides of the valve sleeve. On each side of the valve sleeve, a respective bearing bore accommodating a respective actuator cog, is provided in the adjusting lever.
According to one embodiment of the invention, the drive bearing comprises a bearing ball provided at one end of the adjusting levers and a bearing socket provided on the actuator of the servomotor.
According to a further embodiment, the locating bearing comprises a bearing ball provided at the other end of the adjusting lever, and a bearing socket provided in the valve housing. In addition, the locating bearing may comprise spring elements. The bearing may e.g. be pre-tensioned in one direction via leaf springs which are attached between the housing and the socket. These springs make it possible to obtain cushioning when moving against the limit position as well as to obtain temperature-compensated length equalization, thus maintaining shutoff power, as well as reinforcement or supplementation of the opening movement as a result of the energy stored in the springs. The locating bearing of the coaxial valve may comprise spring elements also so as to compensate for materials shrinkage and tolerances.
Preferably pressure-equalized retention of the valve sleeve in the coaxial valve is provided. Due to such pressure-equalization of the valve, the pressure of the flow medium has no direct influence on the hydraulic power of the valve sleeve.
Furthermore, encapsulation of the valve or the drive may be provided. This provides protection against explosion in the case of gaseous media. Material present as a result of leaks due to improper sealing can be removed from the valve in a controlled way, with the valve also being suitable for aggressive media such as for example MMH and N2O4 (storable fuels).
The valve according to the invention has the advantage that it is xe2x80x9cscaleablexe2x80x9d, i.e. in that the valve can be made in all sizes without principle changes.
Advantageously, the coaxial valve according to the invention is used for temperatures of the flow medium from 3 K (for liquid helium) to 350 K. Furthermore, the coaxial valve according to the invention is advantageously used for pressures of the flow medium of up to 290 bar.
Regulating and shutting off liquid or gaseous flow media, in particular cryogenic, i.e. deep-frozen, media for propulsion of aircraft or spacecraft is a preferred field of application of the coaxial valve according to the invention. Throughout this specification, the term xe2x80x9cflow mediaxe2x80x9d is intended to cover all liquid or gaseous media that may selectively flow through or be shut-off by the present valve.